I see no responses to you yet and I will admit I don’t know the coach or the specific brass fitting you are referring to in your posting. Not all brass alloys are created equal and possibly something in your wiper water mix is reacting to this particular "faux brass" wiper system fitting.
If it is just calcification I would expect the actual wiper arm water jet(s) to be more likely to block from calcification first (especially from only occasional use and using hard water). If it is only the brass fitting that is a consistent problem, you could try a nylon equivalent for the brass if you can find one.....Amazon or eBay might save the day?
__________________
|